Preparation of magnesium-containing silicon alloys



United States Patent 3,094,412 PREPARATION OF MAGNESIUM-CONTAINING SILICON ALLOYS Franz Kaess, Erwin Vogel, and Richard Bauer, Trostberg,

Germany, assignors to Siiddeutsche Kalltstiekstotl- Werke A.G., Trostherg, Germany N0 Drawing. Filed Jan. 24, 1957, Ser. No. 635,973 5 Claims. (Cl. 75-135) The invention relates to a method of making silicon alloys containing magnesium.

Such alloys, particularly magnesium-calcium silicon and magnesium-ferro-silicon alloys, become of increasing importance in the iron industry. They combine the known favorable properties of calcium-silicon and ferrosilicon, such as excellent deoxidizing ability and good separation of slags, with the specific magnesium eifect of crystallizing out, in the manufacture of cast iron, the carbon in the form of nodular graphite.

The alloys have been prepared by combining metallic magnesium with the silicon alloy. Magnesium has been treated in a ladle with the molten silicon alloy or the components have been mixed in the molten state. The magnesium has also been applied in the form of an alloy, whereby the losses of magnesium during the incorporation into the silicon alloy are reduced.

It is a principal object of the invention to provide a method for the incorporation of magnesium into silicon alloys, which method eliminates the difficulties inherent in applying magnesium in the metallic state.

Other objects and advantages will be apparent from a consideration of the specification and claims.

We :have found that magnesium-containing silicon alloys can be readily obtained without the use of metallic magnesium by reacting a molten silicon alloy with magnesia or compositions containing magnesia. If the composition contains also calcium oxide, for instance if dolomite is employed, also metallic calcium is incorporated in the alloy.

The basic reaction between silicon and magnesia is known and has been used for the production of metallic magnesium. However, in the known process, the procedure is based on the continuous shifting of the equilibrium in favor of the formation of magnesium by removing the magnesium vapors by suction or an inert gas, whereupon the magnesium vapors are precipitated as metal.

According to the present invention, the escape of magnesium vapors from the reaction zone has to be prevented, but the reaction is nevertheless carried out in such a way that the equilibrium is constantly shifted in favor of the forward reaction. This result is obtained by the addiiton of basic compounds, such as excess magnesia or calcium oxide, which continuously remove the formed silica in form of slag. The conversion of magnesium to magnesium silicide acts in the same direction.

The reaction can be carried out with any silicon alloy or silicide. Suitable alloys are, for instance, calciumsilicon, ferro-silicon, silico-chrome, silico-manganese and the corresponding silicides.

The reaction temperature depends, of course, on the melting point of the starting alloy. In the reaction with 3,094,412 Patented June 18, 1963 2 ferro-silicon, the melting temperature is in the range of about 1400 C., for calcium-silicon about 10001200 C. During the reaction, the melting point of the alloy is lowered by the magnesium entering the alloy.

By the described procedure, it is readily possible to introduce 1 to 10 percent of Mg into the silicon alloy by melting it with about at least five times the stoichiometric amount of magnesia required by the above equation. For example, if 4.6 percent of Mg shall be introduced, the theoretic amount of MgO to be added according to the above equation would be about parts of MgO by weight for 1,000 parts of a silicon alloy; the amount actually required is at least about five times as large, that isat least about 375 parts.

The amount of added magnesia will depend on the amount of magnesium to be incorporated into the alloy. Generally, the proportion of alloy to magnesia in the melt will be adjusted Within the limits of about 20:1 to 1:1.

The melting process is carried out under cover of an inert protecting gas, such as noble gases, particularly argon. If low melting alloys are used, it may be sufiicieat to perform the reaction under a cover of nitrogen or carbon dioxide. Preferably, the reaction is carried out in closed or partly closed vessels under atmospheric or elevated pressures.

The following examples are given to illustrate the method of the invention. In all examples, the mass was maintained in the molten state in the oven for about 15 minutes, whereupon the obtained molten Mg containing alloy was separated from the silicate slag. All parts are given by weight, unless indicated otherwise. The protecting gas was argon.

Example 1 Starting mixture:

900 parts of calcium-silicon (about 30% Ca and 60% Si) 600 parts of calcined dolomite Obtained alloy: 900 parts Composition: 56.52% Si; 28.83% Ca; 5.05% Mg Example 2 Starting mixture:

900 parts of ferro-silicon (about Si) 600 parts of calcined dolomite Obtained alloy: 1,000 parts Composition: 66.05% Si; 16.56% Ca; 6.00% Mg Example 3 Starting mixture:

1,000 parts ferro-silicon (90% of Si) 500 parts of MgO Obtained alloy: 1,000 parts Composition: 88.90 Si; 4.07% Mg What we claim is:

1. A method of preparing ternary magnesium-containing silicon alloys, comprising adding to a molten silicon alloy containing at least about 60 percent by weight of silicon, the balance being essentially at least one metal selected from the group consisting of calcium, iron, chromium, and manganese, magnesia in an amount of about 5 to percent by weight, calculated on the alloy, heating said mixture above the melting point of said alloy at a temperature of 1000 to 1400" C., whereby part of said magnesia reacts with part of said silicon to form silica and magnesium, which magnesium is bound by unreacted silicon in the reaction mass to form magnesium silicide, whereas said silica forms with other part of said magnesia a silicate slag, and separating said slag from the obtained ternary magnesium-containing silicon alloy.

2. The method as defined in claim 1 where magnesia is added in the form of dolomite.

3. The method as defined in claim 1 wherein calcium oxide is added as additional slag-forming compound.

4. The method as defined in claim 1 wherein said alloy is ferro-silicon.

5. The method as defined in claim 1 wherein said alloy is calcium-silicon.

References Cited in the file of this patent UNITED STATES PATENTS 490,961 Greene et al Jan. 31, 1893 963,345 Willson et al. July 5, 1910 1,869,494 Osborg Aug. 2, 1932 2,194,965 Andrieux Mar, 26, 1940 2,651,569 Loewen et a1. Sept. 8, 1953 FOREIGN PATENTS 199,193 Germany June 23, 1908 464,438 Great Britain Apr. 19, 1937 OTHER REFERENCES Grant: Hackhs Chemical Dictionary, 3rd Edition, 1944, page 529. 

1. A METHOD OF PREPARING TERNARY MAGNESIUM-CONTAINING SILICON ALLOYS, COMPRISING ADDING TO A MOLTEN SILICON ALLOY CONTAINING AT LEAST ABOUT 60 PERCENT BY WEIGHT OF SILICON, THE BALANCE BEING ESSENTIALLY AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF CALICUM, IRON, CHROMINUM, AND MANGANESE, MAGNESIA IN AN AMOUNT OF ABOUT 5 TO 100 PERCENT BY WEIGHT, CALCULATED ON THE ALLOY, HEATING SAID MIXTURE ABOVE THE MELTING POINT OF SAID ALLOY AT A TEMPERATURE OF 1000 TO 1400*C., WHEREBY PART OF SAID MAGNESIA REACTS WITH PART OF SAID SILICON TO FORM SILICA AND MAGNESIUM, WHICH MAGNESIUM IS BOUND BY UNREACTED SILICON IN THE REACTION MASS TO FORM MAGNESIUM SILICIDE, WHEREAS SAID SILICA FORMS WITH OTHER PART OF SAID MAGNESIA A SILICATE SLAG, AND SEPARATING SAID SLAG FROM THE OBTAINED TERNARY MAGNESIUM-CONTAINING SLICON ALLOY. 